Journal of neurophysiology
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1. The purpose of this study was to investigate a proposed role for the postsynaptic dorsal column (PSDC) pathway in mediating visceral nociceptive input into the dorsal column (DC) nuclei. 2. In one group of animals, the hypogastric nerves were sectioned, thereby restricting colorectal input into the cord to pelvic afferent pathways known to coverage on lower lumbar and sacral segments. ⋯ From the results of the studies described in this and the companion paper, we conclude that there is an important pelvic visceral nociceptive pathway involving PSDC neurons that synapse in the NG. The NG in turn activates neurons in the ventral posterolateral (VPL) nucleus of the thalamus. We presume that activation of VPL neurons by noxious visceral stimulation contributes to visceral pain sensation and thus that pelvic visceral pain depends largely on activity in the DC-medial lemniscus system.
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1. The involvement of N-methyl-D-aspartate (NMDA) receptors in thalamocortical transmission has been demonstrated in early postnatal development, but could not be determined so far in adult animals. We used thalamocortical slices from brains of mature mice to examine whether NMDA receptors exist in adult thalamocortical synapses, and what is their potential contribution to thalamocortical synaptic responses. 2. ⋯ All cells that showed a monosynaptic response to electrical thalamic stimulation also exhibited a barrage of mixed synaptic responses to thalamic glutamate application. The amplitude of these synaptic events was dependent strongly on the membrane voltage, and the application of APV to the cortex abolished the events completely. 7. Our results demonstrate that, in adult animals, both thalamocortical and intracortical synaptic pathways utilize NMDA as well as non-NMDA receptors.
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1. Whole cell recordings were performed on the somata of CA1 pyramidal neurons in the rat hippocampal slice preparation Remote synaptic events were evoked by electrical stimulation of Schaffer collateral/commissural fibers in outer stratum radiatum. To isolate non-N-methyl-D-aspartate (NMDA)-mediated excitatory postsynaptic potentials (EPSPs), bath solutions contained the NMDA receptor antagonist, D-2-amino-5-phosphonovaleric acid (D-APV; 30 microM), the gamma-aminobutyric acid-A (GABAA) receptor antagonist, bicuculline (10 microM), and the GABAB receptor antagonists, CGP 35348 (30 microM) or, in some experiments, saclofen (100 microM). 2. ⋯ Because the experimental evidence available so far yields only indirect clues on the strength and distribution of INaP, we allowed considerable variations in these parameters. We also varied both size and location of synaptic input. 7. The major conclusions drawn from these simulations are the following: somatic INaP alone produces little EPSP enhancement; INaP density at the axon hillock/initial segment has to be at least twice the density at the soma to produce substantial EPSP amplification; depending on the density and distribution of dendritic INaP, < or = 80% of a remote synaptic potential arrives at the soma (compared with only 52% in a passive dendrite); synaptic potentials receive progressively more elevation by dendritic INaP the stronger they are; even if restricted to the proximal segment of the apical dendrite, INaP also affects dendritic processing at more distal segments; and spatial distribution rather than local density appears to be the most important parameter determining the role of dendritic INaP in synaptic integration.
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1. Electrophysiological properties of acutely dissociated neurons from the major pelvic ganglion (MPG) of the adult male rat were studied with whole cell patch-clamp recording techniques. The MPG neurons innervating the urinary bladder were labeled by retrograde axonal tracing methods with the use of a fluorescent dye, Fast Blue (FB) injected into the bladder wall and identified with a fluorescent microscope. 2. ⋯ Extracellularly applied TEA (10 mM) suppressed the delayed K+ current by 90%, but suppressed the IA current by only 16%. 6. These results indicate that bladder neurons and unidentified neurons in the MPG have similar properties including a TTX-sensitive Na+ current and three distinct types of voltage-sensitive K+ currents-IA current, Ca(2+)-activating K+ current, and delayed rectifier K+ current-that contribute to the repolarization phase of the action potential. These electrical properties of the MPG neurons resemble those of sympathetic neurons in the superior cervical and inferior mesenteric ganglia.